A titanium oxide having a monoclinic system β-type structure has recently attracted much attention as a high-capacity negative electrode material. The number of lithium ions which can be absorbed into/released from a lithium titanate having a spinel structure (Li4Ti5O12), which has been made practicable, is three per unit chemical formula. For this reason, the number of lithium ions which can be absorbed/released is 3/5 per titanium ion, and the maximum value is theoretically 0.6. Such a lithium titanate having a spinel structure has a theoretical capacity of about 170 mAh/g.
On the contrary, the number of lithium ions which can be absorbed into/released from titanium oxide having a monoclinic system β-type structure is a maximum of 1.0 per titanium ion. This titanium oxide therefore provides a theoretical capacity as high as about 330 mAh/g and a reversible capacity as high as about 240 mAh/g. Consequently, development of high capacity batteries using titanium oxide having a monoclinic system β-type structure is expected.
However, when the titanium oxide having a monoclinic system β-type structure is independently used, adhesion between an electrode and a current collector is poor, which disadvantageously makes it difficult to raise the density of an electrode material layer.